It is thought to be desirable to establish strong cellular immunity to specific pathogens. Repeated administrations with the same vaccine (homologous boosting) have proven effective for boosting humoral responses. However, this approach is relatively inefficient at boosting cellular immunity because prior immunity to the vector tends to impair robust antigen presentation and the generation of appropriate inflammatory signals. One approach to circumvent this problem has been the sequential administration of vaccines that use different antigen-delivery systems (heterologous boosting). This strategy is referred to as “prime-boosting”.
The following are examples of heterologous prime-boost regimens. Those involving a DNA prime include: a DNA prime: DNA prime/bacterial boost (Listeria) against viral antigens (Boyer, et al. (2005) Virology 333:88-101); a DNA prime/bacterial vector (Bacillus) boost, against bacterial antigen (Ferraz, et al. (2004) Infection Immunity 72:6945-6950); a DNA prime/viral vector boost, against tumor antigens (Goldberg, et al. (2005) Clin. Cancer Res. 11:8114-8121; Smith, et al. (2005) Int. J. Cancer 113:259-266); a DNA prime/viral boost against viral antigens (Toussaint, et al. (2005) Vaccine 23:5073-5081; Cebere, et al. (2006) Vaccine 24:417-425; Coupar, et al. (2006) Vaccine 24:1378-1388); a DNA prime/protein boost against viral antigens (Cristillo, et al. (2006) Virology 346:151-168; Rasmussen, et al. (2006) Vaccine 24:2324-2332); a DNA prime/viral boost, against antigens of a parasite (Gilbert, et al. (2006) Vaccine 24:4554-4561; Webster, et al. (2005) Proc. Natl. Acad. Sci. USA 102:4836-4841); DNA prime/adjuvanted protein boost, against tumor antigens (Prud'homme (2005) J. Gene Med. 7:3-17); DNA prime/viral boost plus protein boost, against viral antigens (Stambas, et al. (2005) Vaccine 23:2454-2464); and DNA prime (nanoparticles)/protein boost, against viral antigen (Castaldello, et al. (2006) Vaccine 24:5655-5669).
The following heterologous prime-boost regimens utilize prime compositions not involving DNA: Dendritic cell (DC) prime/bacterial (Listeria) boost, and DC prime/viral boost, against bacterial antigens (Badovinac, et al. (2005) Nat. Med. 11:748-756); bacterial vector prime (Salmonella)/protein boost, against bacterial antigens (Vindurampulle, et al. (2004) Vaccine 22:3744-3750; Lasaro, et al. (2005) Vaccine 23:2430-2438); adjuvanted protein prime/DNA boost, against viral antigens (Sugauchi, et al. (2006) J. Infect. Dis. 193:563-572; Pal, et al. (2006) Virology 348:341-353); protein prime/bacterial vector (Salmonella) boost, against viral antigens (Liu, et al. (2006) Vaccine 24:5852-5861); protein prime/viral vector boost, against viral antigen (Peacock, et al. (2004) J. Virol. 78:13163-13172); Heterologous viral prime/viral boost, using different viral vectors, against viral antigens or tumor antigens (Ranasinghe, et al. (2006) Vaccine 24:5881-5895; Kaufman, et al. (2004) J. Clin. Oncol. 22:2122-2132; Grosenbach, et al. (2001) Cancer Res. 61:4497-4505) Heterologous prime/boost using lipid vesicles, against bacterial antigens (Luijkx, et al. (2006) Vaccine 24:1569-1577).
A reagent that is useful for modulating the immune system is Listeria and particularly Listeria monocytogenes (L. monocytogenes). L. monocytogenes has a natural tropism for the liver and spleen and, to some extent, other tissues such as the small intestines (see, e.g., Dussurget, et al. (2004) Ann. Rev. Microbiol. 58:587-610; Gouin, et al. (2005) Cum Opin. Microbiol. 8:35-45; Cossart (2002) Int. J. Med. Microbiol. 291:401-409; Vazquez-Boland, et al. (2001) Clin. Microbiol. Rev. 14:584-640; Schluter, et al. (1999) Immunobiol. 201:188-195). Where the bacterium resides in the intestines, passage to the bloodstream is mediated by listerial proteins, such as ActA and internalin A (see, e.g., Manohar, et al. (2001) Infection Immunity 69:3542-3549; Lecuit, et al. (2004) Proc. Natl. Acad. Sci. USA 101:6152-6157; Lecuit and Cossart (2002) Trends Mol. Med. 8:537-542). Once the bacterium enters a host cell, the life cycle of L. monocytogenes involves escape from the phagolysosome to the cytosol. This life cycle contrasts with that of Mycobacterium, which remains inside the phagolysosome (see, e.g., Clemens, et al. (2002) Infection Immunity 70:5800-5807; Schluter, et al. (1998) Infect. Immunity 66:5930-5938; Gutierrez, et al. (2004) Cell 119:753-766); L. monocytogenes’ escape from the phagolysosome is mediated by listerial proteins, such as listeriolysin (LLO), PI-PLC, and PC-PLC (see Portnoy, et al. (2002) J. Cell Biol. 158:409-414).
In contrast to the immunotherapy approaches discussed above, in which immunotherapy is used as a primary treatment, adjuvant therapy refers to the use of a secondary treatment prior to (“neoadjuvant”) or following (“adjuvant”) a primary therapy such as surgery or radiation, where the primary therapy is intended to remove or destroy the primary tumor. By way of example, adjuvant therapy may be given after surgery where the detectable disease has been removed, but where there remains a statistical risk of relapse due to occult disease. Adjuvant systemic therapy and radiotherapy are often given following surgery for many types of cancer, including colon cancer, lung cancer, pancreatic cancer, breast cancer, prostate cancer, and some gynaecological cancers.